Last reviewed by the Haute Lawyer editorial team · June 2026 · Profile information is reviewed for accuracy. Learn about our editorial standards →
Mark J. O'Brien
Criminal Defense Lawyer
SILVER MEMBERTampa, FL 33606
Practice Areas
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Verified Haute Lawyer Member · 2026
This attorney has been vetted and recognized by Haute Living as a distinguished legal professional with a proven commitment to legal excellence.
Biography
Mark J. O'Brien is a nationally recognized federal criminal defense attorney with nearly thirty years of legal experience. Managing partner of O'Brien Hatfield PA, he is licensed to practice in Florida (1998), Massachusetts (1998), and Montana (2023), with admissions to the U.S. Supreme Court and numerous federal appellate and district courts. O'Brien began his career as a prosecutor in the Miami-Dade County State Attorney's Office in the late 1990s, rising to felony prosecutor, before founding his law firm in 2002. He now defends individuals and corporations charged with federal and state crimes nationwide, with a focus on white-collar crimes, drug offenses, sex crimes, and criminal appeals. Based in Tampa with offices in Orlando and Miami (Florida) and Billings and Missoula (Montana), O'Brien is widely lauded by federal judges and prosecutors as one of the country's premier defense counsel. He is fluent in English and Spanish.
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Profile last reviewed: June 12, 2026
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Location
Mark J. O'Brien, P.A.
511 West Bay Street, Suite 330
Tampa, FL 33606
In the PressGold
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Frequently Asked Questions
What is Mark J. O'Brien's primary practice focus?
Mark J. O'Brien specializes in federal criminal defense, representing individuals and corporations charged with crimes in federal courts nationwide. His practice includes white-collar offenses (fraud, tax crimes, insider trading, money laundering), drug trafficking, firearms crimes, sex offenses, and criminal appeals at both federal and state levels.
Where is Mark J. O'Brien licensed to practice?
O'Brien holds active bar licenses in Florida (1998), Massachusetts (1998), and Montana (2023). He is also admitted to the U.S. Supreme Court and maintains pro hac vice or direct admissions to federal appellate courts (1st, 2nd, 9th, and 11th Circuits) and federal district courts in over 30 jurisdictions across the United States.
What is Mark J. O'Brien's professional background before criminal defense?
O'Brien began his legal career as a prosecutor in the Miami-Dade County State Attorney's Office in the late 1990s, where he tried over 30 cases to verdict and handled thousands of criminal matters. He rose to the level of felony prosecutor before founding O'Brien Hatfield PA in 2002 to apply his prosecution experience to criminal defense strategy.
What awards and recognitions has Mark J. O'Brien received?
O'Brien has been selected to Super Lawyers (2016–2024), maintains a 10.0 rating on Avvo (Superb), has received the Avvo Clients' Choice Award, and been recognized by Haute Lawyer and other legal directories. Federal judges have commended his advocacy and courtroom skill in published opinions.
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Further Reading & Authority
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